Compactor machines, also variously called compaction machines, are frequently employed for compacting fresh laid asphalt, dirt, gravel, and other compactable materials associated with road surfaces. One such type of compaction machine is a drum-type compactor having one or more drums adapted to compact particular material over which the compactor is being driven. In order to compact the material, the drum-type compactor includes a drum assembly having a vibratory mechanism that includes inner and outer eccentric weights arranged on a rotatable shaft situated within a cavity of the inner eccentric weight. Both amplitude and frequency of vibration are typically controlled to establish degree of compaction. Amplitude is often controlled by a transversely moveable linear actuator adapted to axially bear against an axially translatable key shaft, causing the key shaft to rotate. The rotation of the key shaft in turn alters relative positions of the inner and the outer eccentric weights to vary amplitude of vibration created within the drum. Frequency of vibration is controlled by changing speed of a drive motor positioned within the compactor drum.
To change relative positioning of the inner and the outer eccentric weights, the rotatable shaft typically engages the weights through variously shaped outer surfaces of the shaft. By way of example, U.S. Pat. No. 4,350,460 discloses that the outer surface of a key shaft may be provided with one distinctly shaped, i.e. polygonal, cross-section adapted to engage the inner eccentric weight and another distinctly shaped cross-section to engage the outer eccentric weight for positioning the eccentric weights relative to one another. Those skilled in the art will appreciate that the eccentric weights are normally adapted to rotate together at speeds that approach and/or exceed 4000 revolutions per minute. To assure degree of vibration sufficient to achieve desirable compaction results, some materials require higher frequency vibrations than others. Unfortunately, such vibrations of heavy-duty structures can result in undesirable movements of some parts of such machines relative to adjacent parts. In particular, cylinder rods that may be utilized to rotate the eccentric weights relative to one another may have a tendency to rotate within their associated fixed cylinders, resulting in undesirable wear.
Accordingly, it would be beneficial to provide a system that minimizes wear of actuators and such associated parts. By preventing and/or avoiding premature wear, such system could among other virtues promote reduced frequency of part replacements.